Polypropylene has widely been used in various fields including automobile parts, machine and electric appliances, household commodities, kitchen utensils and packaging films. However, problems have been brought about in that large-sized formed articles are difficult to obtain by, for example, extrusion molding, and in that a high speed molding can scarcely be attained, since polypropylene exhibits lower melt tension (abbreviated hereinafter sometimes as MT). Concretely, the following problems have been encountered:
(1) In blow molding, a phenomenon of "draw-down" due to stretching of the parison by its own weight, causing decrease in the film thickness may be apt to occur, whereby blow molding of large-sized articles, for example, automobile parts, such as bumper and spoiler; and others, such as bottles, is rendered difficult. PA0 (2) In the case of production of sheet or film by a calendering technique, the resulting sheet or film may often suffer from thickness irregularity and, in addition, it has a lower surface gloss. PA0 (3) In the case of production of formed articles by extrusion molding, a high-speed molding may scarcely be practiced and, in addition, large-sized extrusion-molded articles may difficultly be obtained. PA0 (4) In the case of production of vacuum- or pressure-formings from a sheet by a vacuum- or pressure-forming technique, large-sized molded articles are difficult to obtain and, in addition, a deep drawing may difficultly be incorporated. PA0 (5) In the case of production of sheet or film by an inflation molding technique, a poor surface condition may often be encountered, since the balloon may often become unstable. PA0 (6) In the case of producing stretched films, the resulting film may be apt to suffer from occurrence of so-called surging, so that an accident of film breaking upon the stretching may occur and, in addition, the resulting stretched film exhibits a low thickness accuracy. PA0 (7) In the case of producing foamed articles, foaming with a high foaming ratio may difficultly be attained and, in addition, the cells of foamed article are large and coarse with non-uniform cell size. PA0 (1) A technique in which a solution of the magnesium compound (a-1) in a hydrocarbon solvent containing the electron donor (the liquefying agent) (a-3) is brought into contact with the organometallic compound to cause a reaction to precipitate solid matter which is then, or in the course of precipitation, brought into contact with the titanium compound (a-2) to cause reaction. PA0 (2) A technique in which a complex composed of the magnesium compound (a-1) and the electron donor (a-3) is brought into contact with the organometallic compound to cause reaction and, then, the titanium compound (a-2) is caused to contact and react therewith. PA0 (3) A technique in which the contacted product from the contact of an inorganic carrier with an organomagnesium compound (a-1) is brought into contact with the titanium compound (a-2) and with the electron donor (a-3) to cause reaction therebetween. Here, it is permissible to bring the product of contact of the carrier with the magnesium compound into contact with a halogen-containing compound and/or an organometallic compound preliminarily. PA0 (4) A technique, wherein a solid carrier, which is obtained from a mixture containing a solution of the magnesium compound (a-1), the electron donor (a-3) and the carrier in a liquid medium of the liquefying agent and, optionally, a hydrocarbon solvent and on which the magnesium compound (a-1) is supported, is contacted with the titanium compound (a-2). PA0 (5) A technique in which a solution containing the magnesium compound (a-1), the titanium compound (a-2), the electron donor (a-3) and, optionally, a hydrocarbon solvent is brought into contact with a solid carrier. PA0 (6) A technique in which an organomagnesium compound (a-1) in liquid form and a halogen-containing titanium compound (a-2) are brought into contact with each other. In this case, the electron donor (a-3) is used at least once. PA0 (7) A technique in which an organomagnesium compound (a-1) in liquid form and a halogen-containing titanium compound (a-2) are brought into contact with each other, whereupon the resulting product is caused to contact with the titanium compound (a-2). In this case, the electron donor (a-3) is used at least once. PA0 (8) A technique in which an alkoxyl group-containing magnesium compound (a-1) is brought into contact with a halogen-containing titanium compound (a-2). In this case, the electron donor (a-3) is used at least once. PA0 (9) A technique in which a complex composed of an alkoxyl group-containing magnesium compound (a-1) and of the electron donor (a-3) is brought into contact with the titanium compound (a-2). PA0 (10) A technique in which a complex composed of an alkoxyl group-containing magnesium compound (a-1) and the electron donor (a-3) is brought into contact with an organometallic compound, whereupon the resulting product is brought into contact with the titanium compound (a-2). PA0 (11) A technique in which the magnesium compound (a-1), the electron donor (a-3) and the titanium compound (a-2) are brought into contact with each other in a voluntary order to cause reactions therebetween. It is permissible to incorporate a pretreatment of each reaction component before these reactions using a reaction assistant, such as an electron donor (a-3), an organometallic compound, a halogen-containing silicium compound or the like. PA0 (12) A technique in which a liquid magnesium compound (a-1) exhibiting no reducing function is caused to react with a liquid titanium compound (a-2) in the presence of the electron donor (a-3) to deposit a solid magnesium/titanium composite product. PA0 (13) A technique in which the reaction product obtained in the above (12) is further reacted with the titanium compound (a-2). PA0 (14) A technique in which the reaction product obtained in the above (11) or (12) is further reacted with the electron donor (a-3) and with the titanium compound (a-2). PA0 (15) A technique in which a solid mixture obtained by crushing the magnesium compound (a-1), the titanium compound (a-2) and the electron donor (a-3) is treated with any of an elementary halogen, a halogen compound or an aromatic hydrocarbon. In this case, it is permissible to incorporate a process step of crushing either the magnesium compound (a-1) solely or a complex composed of the magnesium compound (a-1) and of the electron donor (a-3) or the magnesium compound (a-1) and the titanium compound (a-2). It is also permissible to subject the crushed product to a pretreatment with a reaction assistant, followed by an after-treatment with, such as, an elementary halogen. As the reaction assistant, for example, an organometallic compound or a halogen-containing silicium compound, may be employed. PA0 (16) A technique in which the magnesium compound (a-1) is crushed and the resulting crushed product is brought into contact with the titanium compound (a-2). Upon crushing and/or contacting the magnesium compound (a-1), an electron donor (a-3) may, if necessary, be employed together with a reaction assistant. PA0 (18) A technique in which a reaction product resulting after the metal oxide, the organomagnesium compound (a-1) and the halogen-containing compound are contacted with each other is caused to contact with the electron donor (a-3) and with, preferably, the titanium compound (a-2). PA0 (19) A technique in which a magnesium compound (a-1), such as a magnesium salt of an organic acid, an alkoxy-magnesium or an aryloxymagnesium, is brought into contact with the titanium compound (a-2), with the electron donor (a-3) and, if necessary, further with a halogen-containing hydrocarbon. PA0 (20) A technique in which a solution of the magnesium compound (a-1) and an alkoxytitanium in a hydrocarbon solvent is brought into contact with the electron donor (a-3) and, if necessary, further with the titanium compound (a-2). In this case, it is favorable that a halogen-containing compound, such as a halogen-containing silicium compound, is caused to co-exist. PA0 (21) A technique in which a liquid magnesium compound (a-1) exhibiting no reducing function is caused to react with an organometallic compound to cause a composite solid product of magnesium/metal (aluminum) to deposit out and, then, the product is reacted with the electron donor (a-3) and with the titanium compound (a-2).
In order to avoid these problems, it has heretofore been practiced to employ such polypropylene reins as given below in which the melt tension is increased:
1) A polypropylene resin composition prepared by blending a polypropylene with a high-pressure low-density polyethylene or with a high-density polyethylene PA1 2) A polypropylene resin having a widely extended molecular weight distribution PA1 3) A modified polypropylene resin which is obtained by slightly cross-linking a polypropylene resin using a peroxide, electron irradiation or maleic acid PA1 4) A branched long chain polypropylene resin which is obtained by introducing long chain branching upon the polymerization of propylene PA1 (A) 10-50% by weight of a higher molecular weight polypropylene part having an intrinsic viscosity [.eta.], determined in decalin at 135.degree. C., of 6-13 dl/g, PA1 (B) 10-89% by weight of a lower molecular weight polypropylene part having an intrinsic viscosity [72 ], determined in decalin at 135.degree. C., of lower than 6 dl/g and PA1 (C) 1-40% by weight of an ethylene/.alpha.-olefin copolymer part having an intrinsic viscosity [72 ], determined in decalin at 135.degree. C., of 0.1-13 dl/g, PA1 polymerizing the monomers in a multistage polymerization of at least three stages in the presence of a polymerization catalyst formed from PA1 a stage of making up a higher molecular weight polypropylene part (A) having an intrinsic viscosity [.eta.] of 6-13 dl/g up to a proportion of 10-50% by weight with respect to the total amount of the finally obtained polypropylene block-copolymer resin, by polymerizing propylene under substantial absence of hydrogen, PA1 a stage of making up a lower molecular weight polypropylene part (B) having an intrinsic viscosity [72 ] lower than 6 dl/g up to a proportion of 10-89% by weight with respect to the total amount of the finally obtained polypropylene block-copolymer resin, by polymerizing propylene, and PA1 a stage of making up an ethylene/.alpha.-olefin copolymer part (C) having an intrinsic viscosity [72 ] of 0.1-13 dl/g up to a proportion of 1-40% by weight with respect to the total amount of the finally obtained polypropylene block-copolymer resin, by copolymerizing ethylene with an .alpha.-olefin. PA1 polymerizing the monomers by a multistage polymerization of at least three stages in the presence of a polymerization catalyst formed from PA1 &lt;&lt;1&gt;&gt; A melt flow rate (MFR), determined according to ASTM D 1238 at 230.degree. C. under a load of 2.16 kg, of 0.01-5 g/10 min., preferably 0.1-5 g/10 min., more preferably 0.3-4 g/10 min. PA1 &lt;&lt;2&gt;&gt; A molecular weight distribution expressed by Mw/Mn (weight-average molecular weight/number-average molecular weight), determined by gel permeation chromatography (GPC), of 6-20, preferably 8-20, and an Mz/Mw (Z-average molecular weight/weight-average molecular weight) of at least 3.5, preferably in the range from 3.5 to 6. PA1 &lt;&lt;4&gt;&gt; A molecular weight distribution of the component (Y) soluble in paraxylene of 135.degree. C. but insoluble in paraxylene of 23.degree. C., held under such a condition that, when the molecular weight distribution curve of the component (Y) on the molecular weight distribution diagram obtained by gel permeation chromatography (GPC) is divided at the maximum peak molecular weight into the higher molecular weight side half and the lower molecular weight side half, the ratio of the surface area S.sub.H for the higher molecular weight side half underlying under the said distribution curve relative to the surface area S.sub.L for the lower molecular weight side half underlying under the said distribution curve, namely, S.sub.H /S.sub.L, is at least 1.1, preferably at least 1.15, more preferably 1.15-2, and the proportion of the surface area for a higher molecular weight portion of molecular weights of at least 1.5.times.10.sup.6 relative to the integral surface area underlying under the entire molecular weight distribution curve is at least 8%, preferably at least 8.2%, more preferably 8.2-40%. PA1 &lt;&lt;5&gt;&gt; A proportion of the 124.degree. C.-eluted segment of the component (Y) soluble in paraxylene of 135.degree. C. but insoluble in paraxylene of 23.degree. C., determined by cross-fractionating chromatography (CFC), of at least 6% by weight, preferably at least 6.5% by weight, more preferably 7-30% by weight, and a weight-average molecular weight (Mw) of the said 124.degree. C.-eluted segment of at least 1.0.times.10.sup.6, preferably at least 1.2.times.10.sup.6, more preferably at least 1.3.times.10.sup.6. PA1 &lt;&lt;6&gt;&gt; A melt tension (MT), determined by flow tester at 230.degree. C., in the range of 5-30 g, preferably 5-20g. PA1 (a) a solid catalyst component based on titanium containing magnesium, titanium, a halogen and an electron donor, PA1 (b) a catalyst component based on organometallic compound and PA1 (c) a catalyst component based on organosilicic compound having at least one group selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and derivatives of them, PA1 (a) a solid catalyst component based on titanium, containing magnesium, titanium, a halogen and an electron donor, PA1 (b) a catalyst component based on organometallic compound and PA1 (c) a catalyst component based on organosilicic compound having at least one group selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and derivatives of them, PA1 (a) a solid catalyst component based on titanium containing magnesium, titanium, a halogen and an electron donor, PA1 (b) a catalyst component based on organometallic compound and PA1 (c) a catalyst component based on organosilisic compound having at least one group selected from the group consisting of cyclopentyl, cyclopentenyl, cyclopentadienyl and derivatives of them. PA1 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, succinic acid peroxide, acetyl peroxide, tert-butyl peroxy(2-ethyl hexanoate), m-toluoyl peroxide, benzoyl peroxide, tert-butyl peroxyisobutyrate, 1,1-bis(tert-butylperoxy)3,5,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxymaleate, tert-butylperoxylaurate, tert-butylperoxy-3,5,5-trimethyl cyclohexanoate, cyclohexanone peroxide, tert-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butyl peroxyacetate, 2,2-bis(tert-butylperoxy)butane, tert-butyl peroxybenzoate, n-butyl4,4-bis(tert-butylperoxy) valerate, di-tert-butyl peroxyisophthalate, methyl ethyl ketone peroxide, .alpha., .alpha.'-bis(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butyl-cumyl peroxide, diisopropylbenzene hydroperoxide, ditert-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, cumene hydroperoxide and tert-butylhydroxy peroxide.
However, these prior art polypropylene resins having improved melt tension exhibit disadvantages in that the formed article produced therefrom reveals inferior appearance and/or lower transparency and in that the stiffness of the resin is insufficient, though occurence of draw-down is made scarce for all these resins. Alternatively, if the molding temperature is elevated in order to effect a high speed molding, problems may be brought about that the resin will suffer from deterioration due to increased heat evolution in the resin, causing higher trend to gel formation (fish eye formation). Moreover, additional process steps of blending of other resin components and an inevitably performed slight cross linking of the polymer by, for example, a peroxide or electron beam irradiation or by using maleic acid or the like makes the process costly.
In Japanese Patent Kokai Hei-9-31299 A, there is disclosed a resin composition of propylene polymers composed of an ethylene/propylene block copolymer component and a higher molecular weight polypropylene component, which is superior in mechanical properties, such as stiffness and surface hardness, and is also superior in the impact resistance. This composition consists of a mixture of an ethylene/propylene block copolymer component having an ethylene content of 0.3-10% by weight and a higher molecular weight polypropylene component having an isotactic pentad fraction of 0.90 or higher, wherein the proportion of a polymer fraction of molecular weights over 5,000,000 relative to the total composition is in the range from 1 to 10% by weight and the proportion of a polymer fraction of molecular weights below 10,000 is 10% by weight or lower and wherein the melt flow rate of the composition is in the range from 0.3 to 50 g/10 min.
Due to the content of the polymer fraction of molecular weights over 5,000,000 in an amount of 1-10% by weight, the resin composition of propylene polymers can provide improvements in the stiffness and in the surface hardness, nevertheless it suffers from problems in that it exhibits inferior flowability upon the melt-molding due to a high content of the higher molecular weight component or due to a content of an ultrahigh molecular weight fraction and in that the appearance of the molded article is inferior due to the quite poor uniformity of dispersion of the higher molecular weight component over the resin composition.
The resin composition of propylene polymers is prepared by melt kneading the ethylene/propylene block-copolymer component and the higher molecular weight polypropylene component, each produced separately of each other, whereby a further problem is brought about in that the production procedures are bothersome and a uniform melt-kneading of these components is difficult.
In WO 98/47959, there is disclosed a resin composition with crystalline polypropylene containing 3-65% by weight of a component soluble in paraxylene of 23.degree. C., 35-97% by weight of a component soluble in paraxylene of 135.degree. C. but insoluble in paraxylene of 23.degree. C. and 0-30% by weight of a component insoluble in paraxylene of 135.degree. C., wherein the said component soluble in 23.degree. C. paraxylene is constituted substantially of an elastomer having an intrinsic viscosity [.eta.] of 0.1-5 dl/g, the said component soluble in 135.degree. C. paraxylene but insoluble in 23.degree. C. paraxylene is constituted substantially of a crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of at least 97%, an Mw/Mn value of 6 or higher and an Mz/Mw value of 6 or higher and the said component insoluble in 135.degree. C. paraxylene is constituted substantially of a filler. In Examples thereof, an elastomer based on styrene and an ethylene/.alpha.-olefin random copolymer are employed for the elastomer and a polypropylene resin having compounded therein a predetermined amount of a polypropylene block-copolymer resin or a higher molecular weight polypropylene resin is employed for the crystalline polypropylene resin.
The above-mentioned resin composition with crystalline polypropylene can be molded into a formed product exhibiting better appearance without occurrence of rashes and is superior in the flexural modulus and in the flowability upon the molding. However, this resin composition is obtainable with a costly and bothersome process, since the polypropylene block-copolymer resin and the higher molecular weight polypropylene resin are produced by polymerization courses independent of each other. In addition, if the amount of the higher molecular weight polypropylene resin to be compounded is increased on melt-kneading them, an increase in the shearing stress will result, whereby a problem is brought about in that it tends to suffering from deterioration of the resin and from insufficient dispersion of the higher molecular weight polypropylene resin in the composition.